This application claims the benefit of Japanese Patent Application No. 10-76649, filed Mar. 10, 1998, which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to receiver technology, and more particularly, to a receiver with an auto gain control circuit of an RF signal.
2. Discussion of the Related Art
A common goal in the art of RF-AGC circuits for use in receivers is to avoid any distortion of an RF amplifier of the receiver. Specifically, when an input signal level exceeds a predetermined level, the gain of an RF amplifier within the receiver is controlled so as to make its output level constant. This control reduces the negative effects resulting from intermodulation (IM).
In most cases, a sufficient attenuation during reception cannot be achieved by controlling the RF amplifier alone. Accordingly, an attenuator is generally disposed within the receiver before the RF amplifier to attenuate the input signal. A sufficient attenuation is made possible by the ability to control both the attenuator and the RF amplifier.
On the other hand, Unexamined Published Japanese Patent Application No. HEI#8-307288 has disclosed another proposal. According to this application, an RF-AGC circuit is constructed which uses an output of an antenna tuning stage along with an output of an RF tuning stage to control attenuation. The output of the antenna tuning stage has a broader band width than the output of the RF tuning stage. This arrangement allows the aforementioned RF-AGC circuit to respond to undesired signals in frequencies away from a desired frequency to be tuned in an effort to minimize distortion resulting from these undesired signals.
FIG. 7 shows the RF-AGC circuit disclosed in the aforementioned Unexamined Published Japanese Patent Application No. HEI#8-307288. Only components relating to this specification are indicated in FIG. 7. An antenna input signal received by an antenna is subjected to band limitation and amplification by a predetermined amount at an antenna tuning stage 1, RF amplifier 2, and RF tuning stage 3, and then input to a mixer (MIX) 4. In the mixer 4, the signal input to the mixer and a signal from a VCO 6 are mixed so as to form an IF signal. The IF signal is supplied to an IF amplifier and FM detector (not shown) at following stages via an IF filter 5. Because the structure and arrangement of such components are well known in the receiver art, a further description thereof is not deemed to be necessary.
In the RF-AGC circuit 33, a control signal is generated according to particular signals within the receiver, each having a different band, and more particularly being the output of the antenna tuning stage 1, the output of RF tuning stage 3, and the output of the mixer 4. The output a of the antenna tuning stage 1, the output b of the RF tuning stage 3, and the output c of the mixer 4 are respectively fetched into amplifiers 7-9 as alternating current (AC) amplifiers and these outputs a-c are respectively amplified by those amplifiers 7-9 and then summed up by an adding stage 25. Then, the amplitude of a signal produced by the above addition is detected by a detecting stage 26. When this detection output level exceeds a reference voltage V5, a drive signal is outputted from the AGC driving stage 28 to the antenna tuning stage 1 and to the RF amplifier 2. The output drive signal is utilized for control of the gain of the RF amplifier 2 and also for control of an antenuator 20 in the antenna tuning stage 1, whereby the output of the RF amplifier 2 is controlled not to exceed a predetermined level.
However, in such a control arrangement, the RF amplifier 2 and the antenna tuning stage 1 are controlled by an output signal a of the antenna tuning stage 1. In such an arrangement, although the control on the antenna tuning stage 1 causes no problem because it is a feedback control, the RF amplifier 2 is not capable of forming a feedback loop. As a result, the control on the RF amplifier 2 becomes excessive so that a large attenuation is produced, resulting in an interruption in the played back sound being caused.
Accordingly, the present invention is directed to a receiver that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is the provision of a receiver having an RF-AGC circuit that controls the RF amplifier in a way that results in an improved continuity of the played back sound.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the receiver includes an attenuator for attenuating an antenna input signal and producing an output signal; a first filter for filtering the output signal of the attenuator and producing an output signal; an RF amplifier for amplifying the output signal from the first filter and producing and output signal; a second filter for filtering the output signal from the RF amplifier and producing an output signal; a first auto gain control circuit including a first auto gain control driving stage outputting a first control signal for controlling the gain of the attenuator; and a second auto gain control circuit including a second auto gain control driving stage outputting a second control signal for controlling the gain of the RF amplifier and for controlling the gain of the attenuator.
In another aspect of the instant invention, the receiver includes an attenuator for attenuating an antenna input signal; a first filter for receiving an output signal from the attenuator; an RF amplifier for amplifying an output signal from the first filter; a second filter for receiving an output signal from the RF amplifier; and a control circuit for controlling an attenuation of the attenuator based on the output signal of the first filter and the output signal from the second filter and controlling a gain of the RF amplifier based on the output signal from the second filter, but not on the output signal from the first filter.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.